A gynecologic ultrasound is usually needed to detect twins when the mother has stopped menstruating for about 40 days. At this time, 2 gestational sacs will be found on the surface of the woman’s uterus. If 2 fetal buds or fetal hearts are found in the sacs at the same time, it is clear that twins are being carried. Since the embryo in the first 3 months of pregnancy is not yet fully developed to form an individual, it is easy for accidents to occur, so parents should pay attention to the fact that prenatal checkups should be strengthened for twins. In addition, generally in pregnancy from the last menstrual period, six to 14 weeks to determine the nature of the chorionic villus of the twin fetus, whether it is a single chorionic villus twins or double chorionic villus twins. Because of the different nature of the chorionic villi the time of termination of pregnancy is not the same.